Safety device for boilers



March 15, 1932. w, MITCHELL 1,849,200

SAFETY DEVICE FOR BOILERS Filed Nov. 6. 1950 3 Sheets-Sheet 1 I 4 E in Q m N l W Fl N iNVENTOR I lfilierflflfilcfzell.

ATTORNEY March 15, 1932. w. H. MITCHELL SAFETY DEVICE FOR BOILERS Filed Nov. 6, 1930 3 Sheets-Sheet 2 iNVENTOR I lferlfim ATTORNEY Ma'rch 1 5, 1932, w. MlTCHELL 1,849,200

SAFETY DEVICE FOR BOILERS Filed Nov. 6, 1930 3 Sheets-Sheet 3 ATTORNEY Patented Mar. 15, 1932 UNITED STATES AL E AB S M CHELL, 0 L LLE ENT'UGKY s nnTY nnvicn non BOILERS Application filed November 6, 1930. Serial No. 493,882;

' My invention relates to the artof steam. boiler construction and particularly tolocomotive and stationary engine boilers whose roof and crown sheets are-held in place by {5 connecting stay bolts; Boilers of this character are prone to explode when the water level over the crown sheet falls so as to uncover the crown sheet particularly at the place where the stay bolts are attached, this 10 being due to the heat softening the metal to a point where the threads between the bolts and crown sheet can no longer hold the steam pressure within the boiler and must give way. Many attempts have, heretofore been made 15 with a view of remedying the situation and to that end fusible plug devices of variouskinds have been proposed for use to open communication between the steam space above the;

crown sheet and the space within the firebox. All such fusible plug devices which have come to my attention have proven unsatisfactory for one reason or another. They are not entirely reliable in their operation.

7 My invention has for an object to provide a si le, inexpensive, positively-acting, and at all times reliable, means for opening up communication between the steam space of the boiler and the inside of the fire box when the water level falls dangerously low. 'The admission of the steam into the'fi're box serves toequalize the temperature on both sides of the crown sheet and'preventsan explosion.

Further,the invention has for its object to provide an auxiliarytstay'bolt for cooperation stress than the regular stay bolts so as to part from the crown sheet first whenflow water H occurs and the crownsheet heats up. W Further, it is an ,object-toprovide what I with a group of ordinary stay bolts in such manner that the auxiliary stay bolt' will part t m'a upe po ay bo fo use in QQQP is ra iv a so ation with hereg lar st ybq without the necessity ofchang-ingin anyway the present design and constructionof boilers d. of the reg ar s y b lt new se he e n, he s perp er bo b i g d s g e to e a l times und g e t s r s th n the eg a tay bolts o the bo l or ther r pose above referred to.

er bj cts wi l i Part be obvi us a d in par e po t out herein t r o he, a ta nm n h for a o ejects and ends, the invention still further re;

sides the novel details of construction,

combination and arrangement of-parts, all

of h c w l b firs f ly des ribed n t e following detailed description, then be par-v ticu'larly pointed vout in the appended claims, referencebeing had to the accompanying I d a ngs, in wh 2,?

Fig re 1 J is 'v ti a ls c on m ha diagrammatic of aportionof a boilerwith the preferred einbodimentof my invention applied. 7 r

' Figure 2 is n n arg d e t a longit dinal section showing the position ofthe parts under normal conditions,

Figure 3 is a view similar to Figure 2 showing the position of, the parts after low water hasocourred and the power bolt has been pulled from the crown sheet.

- 'Figure 4; is a ivie'wsimilar to Figures 2 and 3, showing how the power bolt may be re-seated and held in the crown sheet as'a temporary repair expedient.

Figure 5 is a horizontal sectio on the line 5v5'of Figure 2; r o i Figure, 6 isa vertical longitudinal section of a modification of the invention showing a piston and cylinder. in place of the flexible diaphragm arrangement shown in the preceding'figures, w v 1 V Figur a v t1on of -,a o her 1n0 fication beforeglow water has occurred;

Figure 8 is a similar view of the same em a, :In t e awing i w ich lik num r l of reference indicate like parts in all of the figures, I have illustrated several embodiments of my invention without, however, dosiring to limit myself to these embodiments since other changes in form and detail may be made without departing from the spirit of the invention as outlined in the appended claims.

Referring now particularly to the first embodiment of the invention it will be observed that 1 designates the crown sheet, 2 the fire box chamber, 3 the roof sheet and 1 the ordinary stay bolts now commonly used between the crown and roof sheets of boilers. These bolts have their ends 5 threaded into the respective sheets and then headed as at 6.

The power bolt which constitutes the essence of my invention is designated by 7. It is preferably of the same diameter, material and strength as the regular stay bolts 4 and it has the end, which is adjacent the crown sheet 1, threaded into the crown sheet at 8 and headed at 9 in the same way as the ordinary stay bolts.

The stay bolt 7, however, projects through an aperture in the roof sheet, which aperture is large enough to receive the tapered end 14- of the hollow sleeve 13, the sleeve 13 having a passage or bore 15 of large enough diameter to permit the stay bolt 7 to pass freely through and also to serve as a steam passage from the steam space of the boiler beneath the roof sheet. The upper end of the auxiliary stay bolt 7 is threaded at 10 into a disk 11 and is headed over as at 12. The disk 11 lies above but adjacent to a similar disk 16 on the upper end of the sleeve 13.

17 and 18 respectively designate the lower and upper diaphragms which are preferably composed of flexible material such as copper and these diaphragms 17 and 18 have their centers brazed at 19 or otherwise firmly secured in steam-tight engagement to the disks 16 and 11 respectively. The peripheral portions of the diaphragms 17 and 18 are united by welding as at 20. V

So far as described it will be seen that steam from the steam space of the boiler is at all times free to flow through the passage 15 into the chamber between the dia-- phragms 17 and 18 and tend to expand those diaphragms. The diaphragms are preferably corrugated annularly as shown.

21 are studs carried by the roof sheet to support a cross bar or bridge member 22 which carries a re-setting screw 23 that lines up with the auxiliary stay or power bolt and is adapted to serve the dual function of a stop to limit the upward movement of the bolt 7 when it is released from the crown sheet and to act as a means by which the auxiliary bolt 7 may be again forced downwardly to plug its hole in the crown sheet as a temporary repair. The screw 23 may be worked by a lever or wrench member 24: which normally is tied.

down to the bridge member 22 by a copper wire tie 25, the ends of which are left to project so that the tie may easily be removed by the engineer when necessary.

Referring now to the second embodiment of the invention it will be seen that there is provided a hollow sleeve 26 similar in structure to the sleeve 16 but provided with a cylinder 27 in which a piston 28 works. The piston 28 is carried by the upper end of the auxiliary stay bolt 7 to which it is fastened in the same manner as the fastening of the disk 11 in the preceding embodiment of my invention, it being understood that suitable packing rings 29 are provided to prevent steam escape. The space beneath the piston 28 within the cylinder 27 is in communication with the steam space of the boiler through the passage in the sleeve 26 so that the stem pressure continuously tends to force the pis ton 28 upwardly and applies the excess stress to the auxiliary stay bolt necessary for it to function in the manner desired.

Referring now to the third embodiment of my invention it will be observed that the auxiliary stay bolt in this case is composed 0%. a lower section 30 secured to the crown sheel as before and an upper section 31 secured to the roof sheet, the section 31 having normally an extended end as to receive a wrench by which it may be screwed out to place the power spring 32 under tension, after which the projecting end may be sawed 01? and riveted over to form a head 35.

The opposing end of the stay bolt sections 30 and 31 are connected together by the U- shaped sping 32, the section 31 preferably having a swivel connection 33 with the spring 32.

In all of the embodiments of my invention, it will be observed that provision is made to place the auxiliary stay bolt under a. greater stress tending to pull it out of the crown sheet, than the stress present in the regular stay bolts. Therefore when the crown sheet is subjected to heat the auxiliary bolt being under greater stress will part from the crown sheet before the regular stay bolts are effected to the danger point and release the steam into the fire box through the opening made by the parting of the auxiliary stay bolt from the crown sheet.

A nut or collar 36 may be threaded or otherwise secured (preferably adjustably) on the power bolt 7 and serves a stop by engagement with the hollow sleeve, and by varying the location of the stop on the bolt, the distance that the bolt and plate part may be regulated. in lie'u of using, or in addition to the use of, the screw 23 as a stop. From the above it will be understood that the metal parts of the steam boiler which come in contact with the fire and without proper covering of water, becomes soft and yielding to pressure and separate from each other. The

threads of the stay bolts and those of the hole in the boiler plate where interlocked, will separate. The threads of the iron bolt will strip before the threads ofthe hole in the steel plate, which causes the bolt to become more pointed, (see 37, Fig. 3) and the boiler plate slightly to raise, (see 38 in Fig. 3) at the hole. Thus the hole will be larger at the top part of the plate than at the lower side thereof. This will allow the bolt readily to re-enter the hole when forced into the same in making temporary repairs.

The stop 36 (or the screw 23 as the case may be, or both) is placed so that when the bolt moves upward, parting from the plate, the point end of the bolt does not clear the top edge of the'boiler plate and acts as a guide when the bolt re-enters the hole. This clearance from point of stay bolt to top edge of boiler plate constitutes an aperture which allows the steam to replace the gases of the fire box on the under side of the crown sheet.

The temperature of the steam at boiler pressure is much less than the temperature of the displaced gases which were superheating the boiler at the point of low water; therefore the superheating of the boiler plate and the other (regular) stay bolts will immediately cease and the temperature of the boiler will diminish to the temperature of the steal-n, making the boiler safe. A greater superheating is required at the regular bolts than at the power bolt and plate at the pointof low water, since the ratio of pressure to heat on these regular bolts is less than that of the power bolt.

Metal is fusible under heat and pressure, hence the more heat the less pressure, or the less heat the more pressure is required to make the same change in the shape of the metal. It is this principle that I have taken advantage of in my invention.- 7

In the present case, when the power bolt parts from the boiler plate, due to low water, or when a group of stay bolts become displaced from a crown sheet in a locomotive type boiler, as in a major crown sheet failure from the same cause, the change in theshape which takes place is the tendency of the threads of each bolt to strip where they are interlocked with the screw threads in the hole of the boiler plate.

When the boiler plate has lost this superheat, where the power bolt has parted from it, the downward power applying member 23 can be put in operation, forcing the end of the power bolt back into the hole again, from which it had parted, and pluggingthis hole elfecting temporary'repairs, as 1n the case of a locomotive. The boiler can be fired enabling the engine to complete its trip to the terminal where the power bolt may be put in working order.

While I have shown and described my-in vention for use in connection with boilers having roof and crown sheets held in place by connecting stay bolts, it is obvious that the invention may also be used on other types of boilers such as those having a crown bar supported crown sheet or certain other types that now use fusible plugs as safety devices.

From the foregoing description, taken in connection with the accompanying drawings, it is thought the construction, operation and advantages of my inventionwill be clear to those skilled in the art to which it relates.

\Vhat I claim is:

1. In boilers having crown and roofsheets connected by stay bolts; the combination with a group of said stay bolts, of an auxiliary stay bolt secured to the crown sheet and connected with the roof sheet, and means independent of the crown and roof sheets for constantly applying a greater tensile stress-to said auxiliary bolt than to said ordinary bolts for the purpose described.

2. In combination with the crown and roof sheets of a boiler and a group of rigid stay boltsconnecting the same together; an auxiliary stay bolt'located in association with said group and means independent of the crown and roof sheets for placing said auxiliary stay bolt under greater tensile stress than the normal stress placed on said rigid stay bolts whereby on exposing the stay bolt ends at the crown sheet to excessive heat the auxiliary bolt will part from the crown sheet before the regular stay bolts are suiiiciently weakened to part from the same;

3. In boilers having crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of said regular stay bolts and connected with the crown sheet in the same manner as the regular stay bolts, means independently of the crown and roof sheets connecting said power bolt with the roof sheet and placing said power bolt under greater tensile stress than the stresses carried by the regular bolts at normal times.

. 4. In boilers having'crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of said regular stay bolts and connected with the crown sheet in the same manner as the regular stay bolts, a hollow sleeve secured in the roof sheet and through which sleeve the power bolt passes, and means cooperating with the sleeve and said power bolt and operated upon by steamwithin the boiler for placing said power bolt under greater tension than the tensions of the regular stay bolts.

character, a power bolt associated with a group of said regularstay bolts and connect- 5. In boilers having crown and roof sheets connected by regular stay bolts of uniform ed with the crown sheet in the samemanner as the regular stay bolts, means connecting said power bolt with the roof sheetand for i' placing said power bolt under greater stress than the stresses carried by the regular bolts at normal times, said last named means including provisions tending continuously to pull the power bolt toward the roof sheet and out of said crown sheet.

6. In boilers having crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of said regular stay bolts and connected with the crown sheet in the same manner as the regular stay bolts, means connecting said power bolt with the roof sheet and for placing said power bolt under greater stress than the stresses carried by the regular bolts at normal times, said last named means comprising a hollow sleeve secured to the roof sheet and through which sleeve and spaced therefrom said power bolt passes, disl: members carried respectively by said sleeve and said power bolt and spaced apart, and a flexible chamber comprising connecting walls anchored respectively to said disk members and in communication with the steam space of the boiler via said sleeve for the purposes specified.

In boilers having crown and roof sheets connected by stay bolts; the combination with a group of said stay bolts, of an auxiliary stay bolt secured to the crown sheet and connected with the roof sheet, and means independent of the crown and roof sheets for constantly applying a greater tensile stress to said auxiliary bolt than to said ordinary bolts for the purpose described, and means to re-seat and hold said auxiliary stay bolt in the crown sheet as a temporary repair.

8. In combination with the crown and roof sheets of a boiler and a group of rigid stay bolts connecting the same together; an auxiliary stay bolt located in association with said group and means independent of the crown and roof sheets for placing said auxiliary stay bolt under greater tensile stress than the normal stress placed on said rigid stay bolts whereby on exposing the stay bolt ends at the crown sheet to excessive heat the auxiliary stay bolt will part from the crown sheet before the regular stay bolts are sulliciently weakened to part from the same, and means to re-seat and hold said auxiliary stay bolt in the crown sheet as a temporary repair.

9. In boilers having crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with group of said regular stay bolts and connected with the crown sheet in the same manner as the regular stay bolts, means independently of the crown and roof sheets connecting d auxiliary stay bolt with the roof sheet and placing said auxiliary stay bolt under greater tensile stress than the stresses carried by the regular bolts at normal times, and means to re-seat and hold said auxiliary stay bolt in the crown sheet as a temporary repair.

10. In boilers'having crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of said regular stay bolts and connected with the crown sheet in the same manner as the regulat stay bolts, a hollow sleeve secured in the roof sheet and through which sleeve the power bolt passes, and means cooperating with the sleeve and said power bolt and operated upon by steam within the boiler for placing said power bolt under greater tension than the tensions of the regular stay bolts, and means to re-seat and hold said power bolt in the crown sheet as a temporary repair.

11. In boilers having crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of said regular stay bolts and connected with the crown sheet in the same manner as the regular stay bolts, means connecting said power bolt with the roof sheet and for placing said power bolt under greater stress than the stresses carried by the regular bolts at normal times, said last named means including provisions tending continuously to pull the power bolt toward the roof sheet and out of said crown sheet, and means to re-seat and hold said power bolt in the crown sheet as a temporary repair- 12. In boilers having crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of said regular stay bolts and connected with the crown sheet in the same manner as the regular stay bolts, means connecting said power bolt with the roof sheet and for placing said power bolt under greater stress than the stresses carried by the regular bolts at normal times, said last named means comprising a hollow sleeve secured to the roof sheet and through which sleeve and spaced therefrom said power bolt passes, disk members carried respectively by said sleeve and said power bolt and spaced apart, and a flexible chamber comprising connecting walls anchored respectively to said disk members and in communication with the steam space of the boiler via said sleeve, and means to re-seat and hold said power bolt in the crown sheet as a temporary repair.

18. In boilers having crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of said regular stay bolts and connected with the crown sheet in the same manner as the regular stay bolts, means connectsaid power bolt with the roof sheet and for placing said power bolt under greater stress than the stresses carried by the regular bolts at normal times, said last named means comprising a hollow sleeve secured to said roof sheet and having a cylinder portion, said power bolt projecting through said sleeve, and a piston on said power bolt within said cylinder portion, the space in said cylinder beneath the bottom being in communication with the steam chamber of the boiler.

14. In boilers having crown and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of said regular stay bolts and connected with the crown sheet in the same manner as the regular stay bolts, means connecting said power bolt with'the roof sheet and for placing said power bolt under greater stress than the stresses carried by the regular bolts at normal times, said last named means comprising a hollow sleeve secured to said roof sheet and having a cylinder portion, said power bolt projecting through said sleeve, and a piston on said power bolt within said cylinder portion, the space in said cylinder beneath the bottom being in communication with the steam chamber of the boiler, and manually actuatable means mounted on said roof sheet for forcing said power bolt back to plug its aperture in its head sheet as a temporary repair.

15. In boilers having a roof sheet and a crown sheet connected by ordinary stay bolts, a power bolt connecting said parts and comprising upper and lower sections, one end of each of which is connected respectively to the roof sheet and the crown sheet, and means connecting the other ends of said sections together and applying thereto a stress tending to pull the sections from the sheets, greater in degree than similar stresses present in the ordinary stay bolts.

16. In boilers having a roof sheet and a crown sheet connected by ordinary stay bolts, a power bolt connecting-said parts and comprising upper and lower sections, one end of each of which is connected respectively to the roof sheet and the crown sheet, and means connecting the other ends of said sections together and applying thereto a stress tending to pull the sections from the sheets greater in degree than similar stresses present in the ordinary stay bolts, said means comprising U springs whose legs are secured to the opposed ends of said upper and lower sections of the power bolt. 7

17. In boilers having a fire box wall em braced by an outer wall and enclosing steam and water chambers, stay bolts connecting said walls and including a set of ordinary stay bolts and an auxiliary stay bolt and means placing said auxiliary stay bolt under greater stress than the stress of the ordinary stay bolt continuously to tend, under normal condition, to cause separation of said auxiliary stay bolt and the wall of the fire box,

.the excess stress being suflicient to enable a separation of said auxiliary stay bolt from the fire box wall before the ordinary stay bolts are weakened sufiiciently to separate therefrom under the same temperature conditions.

18. In boilers having crown and roof sheets connected by regular stay bolts of uniform.

character, a power bolt associated with a group of said regularstay bolts andconnect-.

ed with the crown sheet in the same manner as. the regular stay bolts, means connecting saidpower bolt with the roof-sheet and for placing said power bolt under greater strees than the stresses carried by the regular bolts at normal times, said last named means com:

sheet and through which sleeve and spaced therefrom said power bolt passes, disk members-carried respectively by said sleeve and said power bolt and spaced apart, and a flexible chamber comprising connecting walls stress than the stresses carried by the regular I bolts at normal times, said last named means including provisions tending continuously to pull the power bolttoward the roof sheet and out of said crown sheet, and a stop limiting the movement of said power bolt when released from the crown sheet.

20. In boilers having a roof sheet and a crown sheet and suitable means spacing'the crown and roof sheets apart; a power bolt connecting said crown and roof sheets and comprising a stay bolt secured to the crown sheet and connecting with the roof sheet, and means independent of the crown and roof sheets for continuously applying a greater tensile stress to said stay bolt than to the means which holds the roof and crown sheets in spaced relation for the purpose described.

21. In boilers having crown and roof sheets connected by stay bolts; an auxiliary stay bolt located equi-distantly between a group of at least three of said stay bolts and secured the stay bolt ends at the crown sheet to ex- '15 I prisinga hollow sleevesecured to the roof cessive heat will cause the auxiliary stay bolt to part from the crown sheet before the regular stay bolts are sufliciently weakened by the heat to part from the same, substantially as shown and described.

23. In boilers having crown sheets and roof sheets connected by regular stay bolts of uniform character, a power bolt associated with a group of regular stay bolts and being placed between four of said regular stay bolts, means connecting said bolt at its lower end to the crown sheet in substantially the same manner as the regular stay bolts are connected, and means for indirectly connecting the top end of said power bolt with the roof sheet and for placing said power bolt under greater tensile stress than the stresses carried by the regular stay bolts under normal working conditions.

WALTER HARRIS MITCHELL. 

